This invention relates to photographic systems and more particularly, it concerns apparatus for accommodating modified format sizes of photographic sheet film in existing camera systems.
In the camera system marketed by Polaroid Corporation under the trademarks "Polaroid SX-70 Land Camera" and "Polaroid SX-70 Land Film", camera structure and operation are integrated with a container or pack of film in the sense that electric power for camera operation is supplied by a battery packaged with each film pack, a main power switch is closed upon full insertion of the film pack to connect the battery with camera carried electric circuitry, and the film container defines the location of each film unit during exposure relative to the focal plane of the camera. Each film unit in the system carries a supply of processing fluid in an amount calibrated to cover the image format area thereof after exposure and as a result of passage of the film unit between a motor driven processing roller pair supported in the camera. In particular, the processing fluid is spread across the interface between a pair of plastic sheets in each unit, at least one of which plastic sheets is transparent for exposure of a light sensitive layer carried between the sheets and so that the resulting positive photographic image may be viewed.
Because of the construction of each film unit, its exterior appearance is that of a framed photograph in which four marginal edges are defined by paper or other similar material folded about these edges to secure the two plastic sheets in overlying coextensive relationship. The bottom marginal edge of the framed photograph is wide relative to the marginal side and top edges principally because it encloses the pod or supply of processing fluid carried by each film unit. Also, because of the construction of the units, the top wall of the container in which the film sheets are contained is provided with marginal lips dimensioned to substantially cover the framing margins of the photographic film unit including the bottom marginal edge in which the processing fluid pod is located.
In the operation of the system, the uppermost film unit in the container is exposed and then engaged at its rear edge (the top edge of the photograph) by a linearly driven pick and advanced through a slot in the front wall of the container for a distance calibrated to place the leading edge of the exposed film unit (the bottom edge of the photograph) within the nip of the processing roller pair. The rollers then feed the exposed unit forwardly to first rupture the processing fluid pod, spread the processing fluid across the interface between the plastic sheets and finally discharge the exposed and processed unit from the camera.
The outside dimensions of each unit of the presently available "Polaroid SX-70 Land Film" are approximately 89.times.108 mm to provide a substantially square image area approximately 79 mm on the side. The width of the framing margin at the bottom of the photograph is approximately 19 mm whereas the framing margins at the side and top edges of the photograph are approximately 5 mm. While the dimensions of the photograph are well suited for storage in albums or the like, versatility of such systems would be enhanced significantly by a capacity for exposing and processing smaller format photographs, particularly positive transparencies on the order of a 35 mm format for use in a projector designed to handle 2" by 2" slides.
Because of system design, the adaptation of such small format photographs, due to reduced size alone, gives rise to such problems as positioning smaller format film units properly within the existing film well of the camera and accommodation of the smaller format film units by camera carried components such as the camera viewing system, the pick by which each film unit is advanced from the film pack container, the positioning of processing rollers carried by the camera and the like.
Additional problems are associated with adapting the existing system to the formation of positive transparencies. As above-mentioned, the light sensitive materials in which the photographic image is formed in the existing system are carried between two plastic sheets of each film unit. In the standard film unit, the top one of the two plastic sheets is transparent for exposure of the light sensitive layer and for viewing but the back sheet of the standard film unit is opaque. The photochemical materials contained in each standard film unit includes an opacifying agent to protect light sensitve chamicals from ambient light during an imbibition period of several minutes in order to allow complete processing of photographic materials contained in the film unit after the unit is ejected from the camera. Where both plastic sheets of the unit are transparent, as would be required to provide a positive transparency, it is not possible, given the current state of the art, to duplicate the opacifying agent function with chemicals. thus, some provision must be made for protecting the exposed film unit for the imbibition time after it is ejected from the camera.